1. Field of the Invention
The present invention relates to a speaker array apparatus with an improved directivity, and a signal processing method therefor.
2. Description of the Related Art
As a speaker system with an improved directivity, i.e., a narrow directivity, there is for example known a speaker array having a plurality of speakers mounted therein. The speaker array is adapted to control a sound directivity state by controlling the amplitude, phase, and/or other characteristics of sound to be emitted from the speakers, whereby beamed sound can be emitted toward a desired place. Since the beamed sound can be transmitted with less attenuation even to a remote place, the speaker array is often used in a large hall or the like.
On the other hand, since the directivity state control of speaker array involves low- and high-frequency range limits, it is difficult to broaden the sound frequency range of the speaker array. Japanese Laid-open Patent Publication No. 2006-67301, for example, therefore discloses a technique in which the low- and high-frequency range limits are made settable independently of each other to broaden the sound frequency range. Specifically, in this technique, high-frequency range sound is adapted to be emitted from small-sized speakers spaced at a narrow distance from one another, whereas low-frequency range sound is emitted from large-sized speakers spaced at a wide distance. In other words, different types of speakers are selectively used for emission of different frequency range sounds, thereby independently performing the directivity state control for respective frequency ranges. To separate sound into different frequency range components, audio signal for sound emission is divided into signal components of different frequency ranges using a high pass filter (hereinafter referred to as HPF) having a function of permitting the passage of audio signal component for high-frequency range sound while prohibiting the passage of audio signal component for low-frequency range sound, and a low pass filter (hereinafter referred to as LPF) having a function opposite to that of the HPF.
However, the speakers for high-frequency range sounds are small in size, and therefore smaller in maximum possible sound volume than the large-sized speakers for low-frequency range sounds. Thus, there may be considered, for example, to use a method of emitting the entire frequency range sound from the large-sized speakers based on audio signal not passed through the HPF and LPF, and emitting high-frequency range sound from the small-sized speakers based on audio signal passed through the HPF. However, a frequency-dependent change (rotations) occurs in the phase of audio signal before and after the passage of the audio signal through the HPF. As far as the high-frequency range is concerned, the phase of audio signal for high-frequency range passed through the HPF is therefore shifted from that of audio signal for the entire frequency range sound not passed through the HPF, making it difficult to appropriately control the directivity of high-frequency range sound of the entire speaker array.